His moving left and right at the beginning is just to confuse you on which side he will be attacking from. Use the assault shotgun, Magnum, rocket launcher, or MRL to shoot in his mouth. Dodge when he goes underground a few times to attack you. When he comes back up, Carlos or Jill will look up into the sky. Shoot the rocks coming down and repeat the process. He will jump into the air a few times. Shooting his mouth sends him flying to the side. Once his health gets down to half, shoot all four MRL rockets into is mouth. If he lives, finish him off with the assault shotgun. When he throws cars at you, shoot them to make them explode.

In order to defeat him, throw everything you have at him. He has no weak point. Make sure you have a Magnum (level 4), assault shotgun (level 4), and MRL (level 4). Use the Magnum first. After you shoot him enough times, he will jump onto the rooftop and run around to a certain spot, where he will shoot his tentacles down the wall and pop up directly in front of you to attack. This cannot be dodged. He will then jump up and attempt to crush you. Dodge this, and repeat the process. When you run out of ammo for the Magnum and assault shotgun, use the MRL. Shoot all eight rockets at him. If he survives, finish him off with the handgun. Note: He can grab you and hold you in the air. This will damage you until you die or shoot him enough times to make him let you go.

Play Wesker's Mansion Mission (Rebirth).
Repeatedly play the first scenario. Find all three files, then all you need to worry about is time and critical hits. Being a short mission, playing it over and over again is not a bother. Once you get the three files, getting an "S" rank all the time will be easy. Getting all your critical hits is is best right after going up the steps. When the zombies begin moving, aim your crosshair until the red circle blinks and fire for an instant critical.

Every time you see a spawn of small enemies, throw a grenade to kill almost all of them. Get a number of enemy kills at the final score to get an "S" rank on that category.